1. Field of the Invention
The present invention relates to mask patterns and, more particularly, to mask patterns useful for preventing the pattern distortion caused by light transition.
2. Discussion of the Related Art
Development of semiconductor chips, i.e., integrated circuits, has been achieved with technology of the process for micro circuits. Also, due to high packing density and high performance of semiconductor devices, complex structures for semiconductor devices have been introduced. As a result, technology of forming micro patterns in a semiconductor device is highly demanded.
The development in the processing technology of minute patterns has enabled many circuits to be integrated in a given chip area so that heightened packing density and capacitance are brought about and delay time is reduced. Consequently, processing ability is improved.
In 1950s when semiconductor chips were first developed, the micro circuits-processing technology produced 15 .mu.m chips. Currently, chips of submicron of less than 0.5 .mu.m are commonly used. In addition, chips having a line width of less than 0.35 .mu.m are commonly used.
Through the development of the micro circuits-processing, a packing intensity of chips has been doubled for every two years. This trend gets accelerated.
Lithography technique is basic in process for micro circuits. This technique is classified into photo lithography, electron beam lithography, and X-ray lithography.
Generally in case a design rule is more than 0.7 .mu.m, a g line photo stepper having an output wavelength of 436 nm is used. In case of sub-micron lithography technology, an I-line photo stepper having an output wavelength of 365 nm is used. In case of a lithography technology of less than a sub-micron lithography technology, used is an excimer stepper using PSM (phase shift mask) with shifting a light phase by 180 degrees is used. Optical proximity correction mask (OPC) is being considered as a very reliable technology. In this technology, the distortion of an optical lens is corrected, and an original mask pattern is distorted in a direction opposite to the direction of the distortion of a lens. That is, a complementary auxilary pattern is additionally added to each corner of a general mask pattern in order to correct the distortion of a lens.
This technology has an advantage that, since an OPC mask includes a light-shielding layer and a transmitting layer in comparison with a PSM, low production cost, good delivery, and good effectiveness are realized.
Such a conventional mask pattern will be described with reference to the accompanying drawings.
FIG. 1A is a layout of a conventional pattern mask, FIG. 1B illustrates areal image distribution obtained by computer-simulating the mask pattern of FIG. 1A, and FIG. 1C is a graph of distance vs. intensity of light transmitting through the mask pattern of FIG. 1.
As shown in FIG. 1A, a first light-shielding line pattern 2 having a predetermined width is formed on a transmissive substrate 1, and second and third light-shielding line patterns 3 and 4 facing each other are spaced apart from the first light-shielding line pattern 2. Oblong is the center portion C of the first light-shielding line pattern 2 where a center portion C and both edge portions E.sub.1 and E.sub.2 are defined. The edge portions E.sub.1 and E.sub.2 are diagonally connected with the center portion C, and are in symmetry to each other. The second and third light-shielding line patterns 3 and 4 have an oblong form at right angle to one long side D.sub.1 of the first light-shielding pattern line 2. At this time, the space between the second and third light-shielding line patterns 3 and 4 is designated a first space 6 which is at right angle to the long side D.sub.1 of the first light-shielding line pattern 2. That is, the second and third light-shielding line patterns 3 and 4 are oblong in the direction of the space. Fourth light-shielding line patterns 5a and 5b are formed at outer long sides of the second and third line patterns 3 and 4, respectively. And fourth light-shielding line patterns 5a and 5b are spaced apart from the second and third light-shielding line patterns 3 and 4, respectively, by third spaces 8a and 8b, respectively. Short sides D.sub.2 of the second and third light-shielding line patterns 3 and 4 face the long side D.sub.1 of the first light-shielding line pattern 2. The space between the sides D.sub.1 and D.sub.2 is designated a second space 7. The second space 7 horizontally formed is at right angle to the first and second spaces 6 and 8a and 8b. In this case, the ratio of the width W.sub.1 of the first light-shielding line pattern 2 and the width of each of the first, second, and third spaces 6, 7, and 8a and 8b is 2:1.5.
The second and third light-shielding line patterns 3 and 4 are formed to have a width that is almost close to the width W.sub.1 of the first light-shielding line pattern 2. The aforementioned first light-shielding line pattern 2 is used as a mask pattern for patterning gate electrodes.
A conventional mask pattern is a binary mask including a transmissive substrate 1 having almost 100% transmitivity rate and first, second, third, and fourth light-shielding line patterns 2, 3, 4, and 5a and 5b made of a light-shielding material such as chrome. Thus it is advantageous for production cost, delivery, effectiveness, etc.
Referring to FIGS. 1B and 1C, the result of computer simulation and the graph of distribution of light intensity vs distance of the conventional mask pattern shown in FIG. 1a will be described.
In condition that the ratio of the width W.sub.1 of the first light-shielding line pattern 2 shown in FIG. 1A and the width of the first, second, and third spaces 6, 7, and 8a and 8b is 2:1.5, the continuous line, shown in FIG. 1B, indicates an image contour having the same width as the critical dimension (CD) of the first, second, and third light-shielding line patterns 2, 3 and 4. An alternate long and short dash line 12 and an alternate long and two short dashes line 13 and dotted line 14 indicate overexposure. The image contours of the alternate long and short dash line 12 and the alternate long and two short dashes line 13 and the dotted line 14 have light distribution of less than 0.7 which is not related with the resolution of photo resist film (not shown) in the light distribution according to light intensity shown in FIG. 1C. That is, in order that the photo resist film reacts to the exposure light, light having intensity corresponding to 0.7-1 in Y axis should be exposed.
In the aforementioned condition, the peak point in exposing light using first, second, and third mask patterns 2, 3, and 4 is not placed at the center portion A between the first light-shielding line pattern 2 and the second and third light-shielding line patterns 3 and 4, yet moves to sides D.sub.2 of the second and third light-shielding line patterns 3 and 4. Thus the moved peak point A' is at the sides D.sub.2 of the second and third light-shielding line patterns 3 and 4.
In other words, among peak points of light transmitting through the first, second, and third spaces 6, 7, and 8a and 8b, the peak point between the first space 6 and the side D.sub.1 of the first light-shielding line pattern 2 is not placed at 2/D, "A" that is the center of the side D.sub.1 of the first light-shielding line pattern 2 and the edge portion D.sub.2 of the second and third light-shielding line patterns 3 and 4 facing the side D.sub.1. But it is placed at "A'". It is because the compensation for light transmitting through the first and third spaces 6 and 8a and 8b corresponding to the side D.sub.1 of the first light-shielding line pattern 2 is caused.
Referring to FIG. 1B, as the result of the peak point shift, a convex portion "B" is formed at a place corresponding to the first space 6 among the side D.sub.1 of the first light-shielding line pattern 2 in the areal image distribution. Also, the areal image distribution passing through the corners of the second and third light-shielding line patterns 3 and 4 adjacent to the peak point A' by influencing the corners of the second and third light-shielding line patterns 3 and 4 causes proximity effect of increasing the rounding errors, so that it is difficult to pattern desired forms when a photoresist film (not shown) is patterned with an exposure and development process using real mask patterns.
FIG. 2 is a layout of another conventional mask pattern, which looks similar to the mask pattern shown in FIG. 1A. Fourth light-shielding line patterns 5a and 5b formed beside the second and third light-shielding line patterns 3 and 4 formed at one long side of the first light-shielding line pattern 2 are formed to be connected to the second and third light-shielding line patterns 3 and 4, respectively. Accordingly, the third spaces 8a and 8b shown in FIG. 1A don't exist in FIG. 2.
Referring to FIG. 2, a first light-shielding line pattern 22 having a predetermined width is formed on a transmissive substrate 21. Second and third light-shielding line patterns 23 and 24 are formed at one long side of the first light-shielding line pattern 22 and spaced apart from the first light-shielding line pattern 22.
The center portion of the first light-shielding line pattern 22 is designated C and its edge portions are E.sub.21, and E.sub.22. The center portion C has an oblong form. And the edge portions E.sub.21 and E.sub.22 are diagonally connected to the center portion C, and they are in symmetry to each other.
The second and third light-shielding line patterns 23 and 24 are formed at right angle to one side D.sub.21 of the oblong center portion C of the first light-shielding line pattern 22. At this time, a first space 26 between the second and third light-shielding line patterns 23 and 24 is at right angle to the long side D.sub.21 of the first light-shielding line pattern 22.
One side D.sub.22 of each of the second and third light-shielding line patterns 23 and 24 faces the long side D.sub.21 of the first light-shielding line pattern 22. And there is a second space 27 between the sides D.sub.21 and D.sub.22. The ratio of the width W.sub.21 of the center portion C of the first light-shielding line pattern 22, the width W.sub.22 of the second and third light-shielding line patterns 23 and 24, and the width of the first and second spaces 26 and 27 is 2:5:1.5. The first and second spaces 26 and 27 form a T shape.
The peak point of light in performing an exposure process using the conventional mask pattern moves to a direction opposite to the conventional mask pattern of FIG. 1A. That is to say, a light peak point is not at the very center portion between the sides D.sub.21 and D.sub.22, yet moves toward the first light-shielding line pattern 22. As a result, the contour of the side D.sub.21 of the first light-shielding line pattern 22 corresponding to the first space 26 has a concave region (not shown) in performing an exposure process using the aforementioned mask pattern.
The areal image distribution of the aforementioned conventional mask pattern is obtained through experiment using FAIM that is a lithography simulator. The above described problem is generated in light source of less than g-line (436 nm) or I-line (365 nm).
Conventional mask patterns have the following problems Since the peak point of light moves, the CD width of light-shielding line patterns changes and the round error is generated in which the corners of the light-shielding line patterns are rounded, thus deteriorating the reliability of mask patterns in highly packed semiconductor device. Moreover, since the light distribution is uneven, adjacent patterns are distorted.